The invention relates to a disk drive motor for rotating a disk or disks and to a disk storage device in which it is incorporated.
Ordinarily, a stator of a spindle motor of a disk drive has an open-slot construction, in which slot intervals are larger in width than a conductive coil wire. A stator coil is formed in a wrapping system where a tool is inserted into a slot interval and a coil wire is wrapped around a tooth stator tooth coil forming section, or which uses a fitting system where a formed coil is fitted on a tooth. There is also a closed-slot construction described in Japanese Patent Laid-Open No. 54468/1994. A method of forming a coil in this closed-slot construction includes the wrapping system.
In some cases, cogging torque is generated in a magnetic circuit of a disk drive that results in jerking or disrupted rotation. In particular, in attempting to reduce the disk diameter and or the overall shape of a disk and to produce a thin disk drive, it is necessary to increase magnetic forces to ensure the required torque. However, when a magnet producing large magnetic forces is used, for example, a Nd—Fe—B sintering magnet, an intense magnetic field can be generated but the cogging torque problem is also increased. To suppress such cogging torque, it is effective to decrease the radial gaps at the tooth tip ends to smoothly change the magnetic poles as in the above-mentioned prior art.
In using a closed-slot construction, as described in the above-mentioned Japanese Patent Laid-Open No. 54468/1994, in which the tooth are caulked on a connecting part, the closed-slot construction can be fabricated but the increased number of parts causes problems such as increased assembling cost, degradation in durability at connections, increased thickness of the completed disk drive, or the like.
In using an open-slot construction and a wrapping system in which the interval between adjacent tooth slits is decreased to the minimum thickness of a coil wire or less, the coil wire cannot be inserted into the slit, so the slit width must be enlarged by alteration to afford passage of the coil wire. When reworking is carried out to restore the original form, however, an accurate restoration is difficult, so that an area facing a rotor magnet is inevitably decreased. Since the tooth tip ends are opposed to a permanent magnet of a rotor to generate torque, torque is decreased when the area facing the rotor magnet is decreased.
Moreover, since passage by enlarged pieces (minimum slit width) at the tooth tip ends is necessary when using the fitting system, alterations must be made in the same manner as above. That is, in both the closed-slot and open-slot construction, in which slot intervals are equal to or smaller in width than a coil wire, a coil has never been formed without reworking the tooth that constitute a stator core.